1. Field of the Invention
The present invention relates to switching apparatus more particularly switching apparatus for the automatic disconnection of a faulty section and connection of a fault-free section of a remote feed field for devices for alternating current parallel remote feed which are fed from an alternating current source, particularly communication transmission circuits having remotely-fed intermediate stations.
2. Description of the Prior Art
A precaution is to be undertaken with communication transmission circuits having remotely-fed intermediate repeaters or regenerators, referred to below as intermediate stations, so that, given damage to the cable resulting in a short circuit or an interruption in the remote feed circuit, there is no danger to personnel at the location of the fault. It is also advantageous in such a case that the transmission system continues to remain in operation on the line portion from the feed location up to the intermediate station located directly in front of the fault location. The faulty cable field can then be identified through the inherent system locating procedure.
To this end, it is already known (Siemens-Zeitschrift 45 (1971), supplement "Nachrichtenubertragungestechnik", Page 102), given transmission systems whose intermediate stations are remotely fed with a constant direct current in a series circuit, to provide switch auxiliaries in the intermediate stations which, given an interruption of the feed current, close the feed circuit in front of the faulty field. Thereby, a low and, therefore, harmless d.c. voltage is at the fault location. This serves for checking the following cable field and enables the automatic cancellation of the cross connection of the switch auxiliary as soon as the interruption is eliminated, i.e. as soon as a fault-free cable field to the following intermediate station has been reconnected. Given a short circuit of the feed circuit, the d.c. series feed continues to remain operational even without a switch auxiliary; in this case, a hazardous voltage likewise does not occur at the fault location.
In contrast thereto, completely different conditions exist given alternating current parallel feed. With an alternating current parallel feed, continued operation is possible given an interruption of the feed circuit without an auxiliary device; however, conductors at the fault location which can be contacted carry a high remote feed voltage of, for example, 1000 volts. In order to exclude personal hazard, the remote feed must therefore be shut off given such a fault. Therefore, the question is raised as to how a line interruption is to be perceived at the feed location. Given a constant power consumption of the intermediate stations, an interruption results in a corresponding reduction of the remote feed current depending on the position of the fault location. Given a changing power consumption in the intermediate stations, however, the fault recognition from the side of the remote feed can be problematical. Every outage report at the transmission side, even when a fault does not lie in the remote feed path, would then be employed for a shutdown of the remote feed. The question therefore arises as to how the faulty field is to be located when the remote feed must remain shut down for reasons of protection of personnel.
Considerations of the framework of the present invention has shown that it is advantageous when the voltage disconnection of the fault location does not occur in the feed location but in the intermediate station located in front of the fault location. It is advantageous for locating the fault when, given a short circuit in the remote feed circuit, only the faulty cable field is shut off instead of the entire remote feed circuit.